The reactions of di-µ-methylene-bis(pentamethylcyclopentadienyl)-dirhodium(IV) complexes with benzylmagnesium chloride and with alkynylmagnesium chloride; X-ray structure of [(η5-C5Me5)Rh(CH2Ph)(µ-CH2)2Rh(η4-C5Me5CH2Ph)]

Abstract

Reaction of trans-[(C₅Me₅)₂Rh₂(µ-CH₂)₂Cl₂](1) with RCCMgCl gave trans-[(C₅Me₅)₂Rh₂(-µ-CH₂)₂(RC₂)₂](R = Ph or Bu^t). However attack on (1) by benzylmagnesium chloride occurred at one C₅Me₅ ring as well as at one rhodium to give [(η⁵-C₅Me₅)Rh(CH₂Ph)(µ-CH₂)₂Rh(η⁴-C₅Me₅CH₂Ph)](6). The structure of (6) has been deduced by n.m.r. spectroscopy and confirmed by a single-crystal X-ray structure determination which showed the two rhodiums [2.559(3)Å apart] to be linked by two µ-methylene bridges. One rhodium (oxidation state formally +4) bears a σ-benzyl and an η⁵-C₅Me₅ ring; the other rhodium (formally +2) is η⁴-bound to C₅Me₅CH₂Ph where the benzyl on the C₅ ring is exo to the metal. Reaction of [(C₅Me₅)₂Rh₂(η-CH₂)₂(MeCN)₂][PF₆]₂ with R′CCH gave a complex [(C₅Me₅)₂Rh₂(µ-CH₂CHCR′CHCR′CH)]PF₆(7)(R′=p-chlorophenyl); on the basis of the n.m.r. spectra it is proposed that the two rhodiums are linked by a σ,σ,η⁵-CH₂CHCR′CHCR′CH bridge. The mode of formation of these complexes is discussed.